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OpenBet Software Engineer Interview Guide

OpenBet Software Engineer interview guide: reported rounds, questions and how candidates describe the process.

The 60-second brief

A Software Engineer at OpenBet is at the heart of the high-stakes, high-velocity world of sports betting technology. You are not just writing code; you are building the robust, scalable engines that power global betting platforms, ensuring that millions of transactions occur with millisecond precision. Your work directly impacts the reliability and performance of platforms that must function flawlessly during peak global sporting events. This role is inherently complex, requiring a deep understanding of distributed systems, high-concurrency environments, and data integrity. You will work across the full stack or focus on backend systems that handle massive throughput, interacting with product teams and architects to solve real-time engineering challenges.

This guide is scoped to a Software Engineer candidate at OpenBet.

Focus areas

  • Data Structures & Algorithms (DSA)
  • SQL
  • JavaScript

The OpenBet interview process

OpenBet candidates report 4 rounds over 3-5 weeks. The stages below are what candidates describe, not a published process.

Initial Screening

The first stage where candidates are screened for basic qualifications and fit.

What to demonstrate

  • The first stage where candidates are screened for basic qualifications and fit
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Be able to walk your CV end to end in two minutes, and say why this company specifically.
  • Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Technical Evaluations

Deep-dive interviews focusing on practical application, including coding, debugging, and optimization.

What to demonstrate

  • Deep-dive interviews focusing on practical application
  • Including coding, debugging, and optimization

How to prepare

  • Answer aloud and timed: What is a closure in JavaScript, and what is a HOC (Higher-Order Component) in React?
  • Answer aloud and timed: How does a browser work, and what is the DOM?

Peer Interviews

Interviews conducted by peers and team leads to assess technical and cultural alignment.

What to demonstrate

  • Interviews conducted by peers and team leads to assess technical and cultural alignment
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Answer aloud and timed: Explain the difference between GET and POST HTTP requests.
  • Answer aloud and timed: What is a primary key and a foreign key in a database?

Final Technical Deep-Dive

In-depth technical discussions to evaluate advanced skills and problem-solving abilities.

What to demonstrate

  • In-depth technical discussions to evaluate advanced skills and problem-solving abilities
  • Depth in Data Structures & Algorithms (DSA)

How to prepare

  • Answer aloud and timed: How does indexing work in SQL, and when is it not beneficial?
  • Answer aloud and timed: Print Fizz for multiples of 3, Buzz for multiples of 5, and FizzBuzz for both.

Where candidates lose points

Think Out Loud

Always verbalize your thought process while solving problems. This allows the interviewer to see how you approach ambiguity.

Know Your CV

Be prepared to discuss every project listed on your resume in depth. If you claim to know a language or tool, ensure you are ready to answer technical questions about it.

Embrace Trade-offs

There is rarely one "correct" answer in software engineering. When asked to design a system, always discuss the pros and cons of your chosen approach.

Prepare for the "Why

Have clear, professional reasons for why you want to work at OpenBet and why you are looking to leave your current role.

Questions & practice

What is a closure in JavaScript, and what is a HOC (Higher-Order Component) in React?

Medium · Technical & Domain Knowledge

Approach

  1. Say what the runtime actually does before reasoning about the code.
  2. Name what is shared across threads and what owns each piece of state.
  3. Identify the window where an invariant is briefly untrue.
  4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

  • What happens if two callers reach this at the same time?
  • Where could this allocate more than you expect?

Print Fizz for multiples of 3, Buzz for multiples of 5, and FizzBuzz for both.

Medium · Algorithms & Coding

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Write an algorithm to find the shortest path between two words by changing one letter at a time.

Medium · Algorithms & Coding

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Given a set of ranges, write a program that merges any overlapping ranges.

Medium · Algorithms & Coding

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

Reverse a string using your preferred language.

Medium · Algorithms & Coding

Approach

  1. Restate the input: its shape, its size, and what is guaranteed about it.
  2. Name the brute-force solution and its complexity before improving on it.
  3. Choose the data structure from the access pattern, not from familiarity.
  4. State the target complexity and say which constraint rules the naive version out.

Follow-up

  • How does this change if the input no longer fits in memory?
  • What is the worst case, and how likely is it on real data?

How does indexing work in SQL, and when is it not beneficial?

Medium · Technical & Domain Knowledge

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

How would you optimize a slow-running SQL query?

Medium · System Design & Database

Approach

  1. Name the grain you start from and join outward from it.
  2. Check whether any join is one-to-many before aggregating, or the sums inflate.
  3. Say which index the query would use, and what makes it unusable.
  4. Handle the rows that do not match: that is usually the actual question.

Follow-up

  • How does the query change if that join becomes one-to-many?
  • What happens to this when the table is ten times larger?

What is the difference between an object and a class?

Medium · Technical & Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the concepts of inheritance and polymorphism with an example.

Medium · Technical & Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How does a browser work, and what is the DOM?

Medium · Technical & Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

Explain the difference between GET and POST HTTP requests.

Medium · Technical & Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

What is a primary key and a foreign key in a database?

Medium · Technical & Domain Knowledge

Approach

  1. Clarify what is being asked and what a complete answer contains.
  2. State your assumptions explicitly before working the problem.
  3. Say what you would check first and why it is the highest-information step.
  4. Work from the requirement backwards to the design.

Follow-up

  • What assumption would you test first?
  • How would you know your answer was wrong?

How would you design a web crawling algorithm?

Medium · Algorithms & Coding

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

How would you develop a service similar to Bitly?

Medium · System Design & Database

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Design a database schema for a library system.

Medium · System Design & Database

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Explain how network connections are established and how URLs and IP addresses interact.

Medium · System Design & Database

Approach

  1. Fix the scope first: who calls this, how often, and what they do when it fails.
  2. Name the read and write paths separately; they rarely have the same bottleneck.
  3. Choose a partition key and say what query it makes expensive.
  4. State the consistency you need, and where you are willing to be stale.

Follow-up

  • What breaks first when traffic grows ten times?
  • How does this behave when that dependency is down for an hour?

Exports duplicate a row range about once a week

Hard · leases · clock skew · idempotency

Roughly once a week an export writes a file containing a duplicated range of rows. The affected job_run rows show attempt = 1, status = succeeded, one started_at, and a lease_owner naming a different host from the one whose logs show the job starting. Leases last 30 seconds and are heartbeated every 10 from inside the handler; lease_expires_at is computed on the worker and compared against the database's now(). Find the mechanism, and give a fix that holds even if you cannot fix the clocks.

Approach

  1. Start from the fact that eliminates the obvious answer. attempt = 1 means no retry was recorded, so this is not a re-run after failure; two workers ran the same row concurrently and the takeover path never touched the counter. lease_owner naming a host other than the one that started the job is the same statement from the other side.
  2. Enumerate the mechanisms that cause a premature takeover, then find the signal that separates them. Either the lease genuinely expired because the heartbeat did not fire, which is what happens when the heartbeat runs on the handler's own thread and the handler makes a long blocking call, or it only appeared expired because two clocks disagree, since lease_expires_at is written from the worker's clock and evaluated against the database's. The discriminator is the distribution: incidents clustered on the longest exports indict the heartbeat, incidents clustered on one host indict skew. Measure both, and measure each host's offset against the database directly.
  3. Read the reclaim query precisely. In PostgreSQL now() is transaction start time, not statement time, so a reclaimer holding a long transaction compares against an older timestamp than expected; clock_timestamp() is the statement-time function. This is worth ruling in or out before you redesign anything, because it changes which rows look expired.
  4. Remove the second clock rather than trying to synchronise it. Issue and extend the lease in the database, with lease_expires_at = now() + interval '30 seconds' in both the claim and the heartbeat, so exactly one clock is ever compared and worker skew stops mattering to this predicate.

Follow-up

  • The displaced worker has already streamed half the file to object storage. What makes that side effect safe to repeat?
  • You now count takeovers. What alert fires on that counter, and at what threshold?

Suggested practice checklist

Built from the rounds and topics OpenBet candidates report.

Day 1 — Map the OpenBet loop

  • Write out the reported sequence: Initial Screening, Technical Evaluations, Peer Interviews, Final Technical Deep-Dive.
  • For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 4 reported rounds, with the weakest marked.

Day 2 — Work Data Structures & Algorithms (DSA)

  • Spend the session on Data Structures & Algorithms (DSA), which OpenBet candidates report being tested on.
  • Write one worked example in Data Structures & Algorithms (DSA) and time yourself on it.

Deliverable: One timed worked example in Data Structures & Algorithms (DSA).

Day 3 — Work SQL

  • Spend the session on SQL, which OpenBet candidates report being tested on.
  • Write one worked example in SQL and time yourself on it.

Deliverable: One timed worked example in SQL.

Day 4 — Work JavaScript

  • Spend the session on JavaScript, which OpenBet candidates report being tested on.
  • Write one worked example in JavaScript and time yourself on it.

Deliverable: One timed worked example in JavaScript.

Day 5 — Answer out loud: Technical & Domain Knowledge

  • Answer aloud, timed: What is the difference between an object and a class?
  • Answer aloud, timed: Explain the concepts of inheritance and polymorphism with an example.

Deliverable: Spoken answers to 2 reported Technical & Domain Knowledge question(s), under time.

Day 6 — Answer out loud: Algorithms & Coding

  • Answer aloud, timed: Print Fizz for multiples of 3, Buzz for multiples of 5, and FizzBuzz for both.
  • Answer aloud, timed: Write an algorithm to find the shortest path between two words by changing one letter at a time.

Deliverable: Spoken answers to 2 reported Algorithms & Coding question(s), under time.

Day 7 — Answer out loud: System Design & Database

  • Answer aloud, timed: How would you develop a service similar to Bitly?
  • Answer aloud, timed: Design a database schema for a library system.

Deliverable: Spoken answers to 2 reported System Design & Database question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Tell me about yourself and your professional journey.

Medium · Behavioral & Situational

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Why are you interested in working for OpenBet?

Medium · Behavioral & Situational

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Your manager assigns an urgent task, but another team lead assigns a different high-priority task. How do you

Medium · Behavioral & Situational

Your manager assigns an urgent task, but another team lead assigns a different high-priority task. How do you handle this conflict?

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?

Describe a recent project you contributed to in detail.

Medium · Behavioral & Situational

Approach

  1. Pick a story where you made the decision, not one where you watched it.
  2. State the situation in two sentences and spend the rest on the reasoning.
  3. Give the blast radius: what could have broken, and what you measured.
  4. Name the disagreement and how you resolved it with evidence.

Follow-up

  • What would you do differently if you ran that again?
  • How did you know your change caused the improvement?